1. Field of the Invention
The present invention relates to a method for detecting excessive burn (excessive burning state) during a regeneration process of a particulate filter disposed at an exhaust passage of a diesel engine.
2. Description of Related Art
Exhaust gas of a diesel engine includes particulates, which are exhaust particles of mainly carbon. The particulates cause black smoke in the exhaust gas. Thus, there is provided an exhaust gas purifying apparatus, in which a honeycomb ceramic particulate filter is provided in an exhaust passage of the diesel engine to collect the particulates with the filter.
The filter of the exhaust gas purifying apparatus is clogged with the particulates attached thereto with the passing of time. As a result, pressure in the exhaust passage increases thereby degrading an engine output and a fuel economy.
Therefore, there is proposed a method for automatically sensing the clog of the filter to regenerate the filter by burning the collected particulates.
A method for providing a burning state (method for burning the particulates) includes, for example, providing an intake air throttle valve upstream of the engine. In this method, the intake air is reduced to increase exhaust gas temperature of the engine, thereby the particulates are burned. Also, another method for providing the burning state includes mixing the exhaust gas with unburned gases such that the hydrocarbon (HC) in the unburned gases reacts with an oxidation catalyst to increase the exhaust gas temperature. Thus, the particulates are burned. (see Japanese Unexamined Patent Publication No. 2001-207830).
When the collected particulates are burned and removed, the temperature in the filter increases due to the burning. At this time, the filter may be melted and damaged when, for example, the particulates are partially accumulated in the filter to cause excessive burn. Therefore, to limit the filter from breaking due to the excessive burn, there has been utilized a method for determining whether excessive burn (excessive burning state) occurs by monitoring the exhaust gas temperature downstream of the filter.
However, the temperature features in having a relatively large time constant so that there is a delay before the exhaust gas temperature notifies a change of the burning state of the particulates. In other words, even when the excessive burn occurs due to the regeneration process, it may take a certain amount of time before the change of the exhaust gas temperature is detected. Thus, the regeneration process may be excessively continued for more than a necessary period and a risk for melting and damaging the filter due to the excessive burn may be enhanced.